1. Field of the Invention
This invention relates to a length measuring device, in particular to a length measuring device which makes it possible to directly read a length of two sides of a bent member from a virtual intersection of the extension lines of two sides of a bent member folded with an arbitrary angle, wherein "the virtual intersection of two faces" means an intersection at which the extensions of two outer surfaces extending along the respective sides intersect each other in a meeting area (a bent area).
2. Description of the Prior Art
In plate processing, there are many cases where the processing of bent member A formed of two or more sides is made. However, since the bent member A is made by bending a plate, a bent area in which two sides A1, A2 of bent member A as shown in FIGS. 1(a), 1(b) meets is not formed into an acute angle, but formed into a curved form.
On the other hand, in the instruction in the drawing in plate processing, dimensions L1, L2, L3 from an intersection P of extension lines of two faces of a bent member is shown. However, since the actual bent area of the bent member is curved, it is impossible to directly read the length from the virtual intersection P the virtual an actual article.
In the inspection of bent member, it is needed to measure dimensions L1, L2, L3. In a conventional job site, a board is put on one side for which measurement is made, while the other side is located on a holder, and a measurement of a length between the board and the upper surface of the holder is made using a vernier caliper. However, using this method, only an approximate value is obtained. Further, recently, three-dimensional measuring device and others appear, by which dimensions of from an intersection can be measured. However, the three-dimensional measuring device is extremely high in cost so that it cannot be easily applied.
Further, when bending a plate so as to form a desired bent member, it is useful to know the respective dimensions (developed dimensions) of both straight faces and the bent area of the bent member formed from the plate. For example, developed dimensions corresponding to a bent member shown in FIG. 1(a) are as shown in FIG. 2. Therefore, if a ratio of dimension L to dimension L1, L2, which is dependent on a bending angle and a thickness of plate, is known, it is possible to know developed dimensions of plate by knowing dimensions L1, L2. To preset developed dimensions is specially useful for locating holes bored in a plate at a given position in a bent member.